Graphic Organizers are important tools for writing. They help students plan out their writing and give direction and planning. There are many apps and web sites out there to use. Below are just 2 that I was looking at while doing the 21 Things 4 Teachers course. Check them out for yourself!
Popplet is a great graphic organizer for story development and other writing. It is easy to use (and has an iPad app). This is a tool to help plan paragraph writing or make any graphic organizer you may need. It offers many options to make it fun and is "kid friendly" for elementary teachers/students.
Gliffy is another graphic organizer. I don't like this a much as Popplet, but it is another option. It is easier to make things in specific location with the grid lines in the background.